1. Field of Disclosure
This invention relates to valves, and more particularly to shuttle valves.
2. Background
Subsea wellheads are often relied upon during deep water exploration for oil and natural gas. Subsea drilling operations may experience a blow out, which is an uncontrolled flow of formation fluids into the drilling well. Blow outs are dangerous and costly. Blow outs can cause loss of life, pollution, damage to drilling equipment, and loss of well production. To prevent blowouts, blowout prevention (BOP) equipment is required. The subsea wellheads include a stack of BOPs. Annular BOPs are actuated on a routine basis to snub or otherwise control pressure during normal drilling operations. Other blow-out preventers, such as blind rams, pipe rams, kelly rams and shear rams will also be included in the stack on the subsea wellhead. When these types of rams are actuated, operations in the well cease in order to control pressure or some other anomaly. Blind rams, pipe rams, kelly rams and shear rams are periodically tested to make sure that they are operational.
The well and BOP connect to the surface drilling vessel through a marine riser pipe, which connects to the BOP through a Lower Marine Riser Package (“LMRP”) that contains flow control devices to supply hydraulic fluids for the operation of the BOP. The LMRP and the BOP are commonly referred to collectively as simply the BOP. Many BOP functions are hydraulically controlled, with piping attached to the riser supplying hydraulic fluids and other well control fluids. Shuttle valves attached to each BOP, as in U.S. Pat. Nos. 4,253,481 and 6,257,268 have been used for many years to control the flow of hydraulic fluid.
It is important that underwater shuttle valves used in connection with operation of subsea blowout preventers (BOPS) act properly because of the importance of their function and their inaccessibility. In emergency situations or during testing, it may be necessary to close the subsea BOPs using an alternate low flow circuit, a test pump, or in extreme situations a remotely operated vehicle (ROV). The ROV is an unmanned submarine with an on-board television camera so the ROV can be maneuvered by topside personnel on board a ship or platform. The ROV is equipped with a plug that stabs into a receptacle on the ROV docking station on the BOP stack. Tubing runs from the receptacle on the ROV docketing station to a biased shuttle valve.
The ROV is maneuvered to stab into the receptacle on the ROV docking station. The ROV uses a hydraulic pump to inject hydraulic fluid at relatively high pressures (greater than 1,000 psi) and relatively low flow rates into the hose to the biased shuttle valve to close the BOPs.
The Gilmore Valve Company pressure biased ROV shuttle valve with metal-to-metal seal as described in U.S. Pat. No. 6,257,268 is a current solution to allow a low flow (such as an ROV) to control a BOP Ram. Unfortunately this valve is very sensitive to reverse flow (one way flow), and in combination with the requirement of the metal-to-metal seal to stay rigidly seated not to leak, the valve will fail to provide BOP ram control from a low flow supply source like an ROV.
The high pressures and low flow rates required by a ROV mandate use of a low volume positive displacement pump. These are similar to a bicycle pump. Stroking forward pushes the fluid through an outlet check valve. When the stroke ends the flow stops and the outlet check valve closes. At this point the pump plunger is reversed back to the start position for another stroke and refilling of fluid into the stroking chamber from the pump inlet check valve. During the return stroke of the bike pump if the outlet check valve leaks ever so slightly, the line pressure on the outlet of the pump will decay because a small amount of fluid flowed back into the bike pump stroking chamber.
This is the scenario where the Gilmore valve will get into a situation of the shuttle lifting off of the inlet seat and dumping fluid. This creates a vicious cycle with the function port never obtaining pressure to actuate a function. This is a disadvantage of a “one way” communication at the ROV inlet port. This is also a disadvantage in the “blocked” situation, when the ROV disconnects by closing a valve to block in the pressure on the ROV inlet port of the valve, as a small leak will make the valve “dump” all of the function pressure/fluid back through the opposing inlet port. Another problem is that the flow volume from the ROV pump is not high enough to over come the leak rate of the metal-to-metal seat attempting to close the opposing inlet port. This type of seat in practice will leak until there is a substantial hydraulic force (via pressure acting on the area of the seat) pushing it firmly closed enough to make metal-to-metal contact completely around the perimeter of the seat. Until this force is exceeded, the valve will leak.
The valve exemplary embodiments herein described do not rely on a check valve (one-way communication) or metal to metal seat to maintain positive sealing and remain in control of the function pressure even when there is a decay in pressure or when closed when pressure is supplied to the function port and the ROV valve is blocked off.